120 



REVOLVING CONDUCTING WIRES. 



movements, by using numerous circuits of conduct- 

 ing-wire in an oblong coil between 'the two poles of 

 a horse-shoe magnet, as represented in Fig. 39, with 

 the addition of the usual current-changer, com- 

 posed of two elastic springs connected with the 



oblong coil. This current- 

 changer reverses the direc- 

 tion of the circuit at every 

 half-revolution, and thereby 

 sustains a continuous pro- 

 pulsion to augment the 

 electro-motive power. Mr. 

 Davis says : " This instru- 

 ment revolves with the 

 wonderful velocity of more 

 than six thousand rota- 

 tions per minute, and pro- 

 duces a loud humming 

 sound, audible at a consid- 

 Fi *- 39> erable distance." 



Ampere, De la Rive, Wollaston, and other in- 

 vestigators in electro-dynamics, suggested various 

 theoretical relationships of electric 

 and magnetic currents for produc- 

 ing resultant movements, which 

 appear to have been verified with 

 mathematical precision. Faraday, 

 with his persevering sagacity, suc- 

 ceeded, in the year 1821, in exhib- 

 iting a conducting-wire revolving 



Fig. 40. 



